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I. Two experiments were conducted to determine the effects of heat on the nutritional value of lupin (Lupinus ungustifolius cv. Uniharvest and Unicrop)-seed meal, relative to soya-bean meal, for growing pigs.2. In both experiments, values for carcass gain/d and food conversion ratio (FCR) on a carcass basis of pigs fed on the diets containing lupin-seed meal were inferior (P < 0.05) to those produced by pigs fed on soya-bean meal.3. In the first experiment, heating lupin seed at temperatures from 105 to 150" for 15 min resulted in a linear depression in carcass gain/d, a quadratic increase in carcass FCR, a linear decrease in lean in the ham and a linear increase in backfat thickness. In the second experiment, autoclaving lupin seed from 5 to 45 min at 121" resulted in a linear depression in carcass gain/d and a linear increase in carcass FCR.4. The addition of L-lysine to the diets containing lupin-seed meal verified that lysine was limiting in both experiments. The additions of L-lysine did not overcome the differences in carcass gains/d of pigs fed on lupin-seed meal relative to those fed on diets containing soya-bean meal.5. It is concluded that the low lysine availability in lupin-seed meal for pigs is not due to the presence of heat-labile anti-nutritional factors in the seed.Previous work (Batterham et al. 1984) indicated low and variable lysine availability in lupin (Lupinus angustifo1ius)-seed meal for growing pigs. Lysine availability (proportion of total) varied from 0.37 to 0.65 (mean 0.53) in four samples. The low lysine availability was not due to impared digestibility as the ileal digestibility of lysine in the sample with lowest lysine availability (0.37) was high (0.86; M. R. Taverner, personal communication). Furthermore, the low lysine availability was specific to pigs as it was high in rats (mean 0.8 1, range 0.70-0.94; Batterham et al. 1984) and chicks (mean 0.91, range 0.81-0.95; E. S. Batterham and E. J. Major, unpublished results). The low lysine availability in pigs appeared to be due to either the lysine being digested in a form that was inefficiently utilized or to the presence of anti-nutritional factors that depressed pig performance in the slope-ratio assays.The major proportion of lupin-seed protein is storage protein, globulins (Cerletti, 1983). The protein is deficient in the sulphur amino acids, methionine and cystine. In vitro digestibility of lupin globulins with pepsin and trypsin is less than that of casein, possibly due to the native configuration of the protein molecule, and is improved by heat (Cerletti, 1983). As a result, Cerletti (1 983) concluded that both amino acid composition and reduced digestibility by proteolytic enzymes contributed to the poorer nutritional value of lupinseed protein.Lupin seeds appear to be free of the major anti-nutritional factors, trypsin inhibitors and haemagglutinins (Hill, 1977;Hudson, 1979) and are fed without heat processing. Older 'bitter' varieties contain up to 25 g alkaloids/kg. Newer 'sweet' varieties are virtually free of alkaloi...

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